Merlin waits for Arthur. It's his destiny, his promise. But he doesn't go through all those centuries alone—not completely. There are positives to this time, as slowly Merlin learns to finally accept rewards for everything he has done. This takes time, since he deserves the great rewards that aren't in the easily recognizable form of knighthood and handshakes and gold.
*A/N I wrote this fairly quickly, without that much editing or planning, so I apologize. I do hope to edit and better flesh it out later, but for now, I still hope you enjoy!*